Conventionally, as a display device, an organic EL display device (Organic Electroluminescence Display) using an organic electroluminescence material (organic EL material) in a light emitting element (organic EL element) of a display part is known. Unlike a liquid crystal display device or the like, the organic EL display device is a so-called self-light emitting type display device which realizes a display by causing the organic EL material to emit light.
In a top emission type organic EL display device, a microcavity structure which utilizes a resonance effect of light between a reflection electrode as a pixel electrode and a semitransparent electrode as a counter electrode is generally used. In the microcavity structure, EL spectrum peak wavelengths of each color of red, green, and blue (RGB) are made to coincide with an optical path length between the pixel electrode and the counter electrode, and the film thickness of an organic layer between the pixel electrode and the counter electrode is changed in order to extract the strongest light from each color. In this way, it is possible to resonate and emphasize only light having a wavelength which coincides with the optical path length, and it is possible to weaken light having a wavelength which has a misaligned optical path length. Therefore, the spectrum of light extracted to the exterior becomes high intensity, and luminosity and color purity are improved.
In recent years, a structure in which a film for adjusting an optical path length is also arranged above the semitransparent electrode has been examined in order to further improve the efficiency of a display device. For example, a structure has been disclosed in which a high refractive index film and a low refractive index film are alternately stacked above a semitransparent electrode (for example, Japanese Laid Open Patent publication No. 2014-56666).